Sublethal insecticide effects on the probing responsiveness of tsetse flies and blowflies

ABSTRACT. Tethered Glossina austeni Newst. males and females were tested for daily and starvation-related changes in their probing responsiveness to a warmed sponge surface presented to their tarsi. The change in responsiveness of the two sexes was indistinguishable, both following a marked V-shape pattern across the photophase of LD 12:12 and an increase from a mean of c. 5% responding on day 3 after a blood-meal to over 60% doing so on day 6. Sublethal doses ( c. LD₁₅) of endosulfan had no detectable effect on this pattern, but of DDT caused a temporary doubling of responsiveness, and of permethrin caused a marked and long-lasting reduction in responsiveness. Tethered Protophormia terraenovae (R.-D.) tested similarly for changes in threshold to tarsal stimulation with sucrose solutions (assessed by whether or not they extended the proboscis), showed a marked threshold decrease following LD₁₅ diazinon treatment and, like the tsetse, no effect of LD₁₅ endosulfan treatment, though unlike tsetse they showed no increase in threshold following permethrin treatment. The results are discussed in relation to what is known of the mode of action of these four insecticides, and in relation to circadian rhythm physiology in insects.